This invention relates to a waterborne twin hull vessel design, specifically to the improvement of hull stability and performance.
Vessel hull stability is dependent on the location relationship of the hull""s center of buoyancy (displacement) and the loaded hull""s center of gravity. The center of buoyancy is defined as the mathematical central point location of the water displaced by the hull""s shape, and the center of gravity of the loaded hull is defined as the mathematical central point location of the weight of the hull together with its cargo. Both are measured along both the vertical and horizontal axis.
When a vessel is at rest or transitioning in calm water the center of gravity and center of buoyancy are in the same vertical position. When a wave hits the vessel, the change in displacement caused by the wave""s form against the hull will shift the centers of gravity and buoyancy away from each other temporarily until a new equilibrium can be reached. On board the vessel this law of nature is experienced as a pitching or rolling motion. Under severe conditions, this can be very uncomfortable and may lead to sea sickness.
Another way to describe this phenomenon is that a vessel at rest in the water displaces the volume of water which equals its weight. When a vessel moves through the water and a wave passes against it, the height of this wave will ride up the sides of the vessel. At this point, the vessel displaces more water than it weighs, thus rising up in an effort to equalize its (vessel) weight with that of the water. Rising very quickly, it over compensates and finds itself not displacing enough water and descends back into the water. In rough seas this motion is repeated continuously in a violent manner.
The rising and falling of the waves along the sides of the vessel are called inches of immersion. For example, if a vessel displaces 1,000 pounds per inch of immersion, then a 12 inch or one foot wave will exert 12,000 pounds of lift on the vessel. The same is true with the trough of the wave as it recedes from the hull of the vessel. The craft will fall into the hole left by the receding wave.
The search for a vessel to tame the effect of the ocean waves has challenged man since the beginning of time. Vessel designers have continued to make advancements aimed at minimizing a wave""s effect on hull motion. The easiest solution is to build a vessel large enough so that even a large wave will have a minimal influence on buoyancy. Other methods of approaching the problem include the design of submarines, hydrofoils, hovercrafts, ground effect crafts, catamarans, and swath vessels. Some of these vessels work very well at reducing the effect of ocean waves; however, some are cost prohibitive to build and operate.
Submarines, while on the surface of the ocean, are victims of the waves and swells of the ocean. However, once submerged beneath the surface, wave action is minimized. Unfortunately, submergence is not often a feasible method of water transportation due to factors related to practicality and cost effectiveness.
Hydrofoils are another alternative and have been around almost as long as the telephone. The United States Navy has spent considerable time and money on hydrofoils with limited success, but eventually abandoned its efforts due to the high cost of operation and maintenance.
Hovercrafts are still being pursued around the world and have yielded good results in calmer, sheltered waters of coastal zones. The hovercraft rides on a cushion of air which allows the waves to rise and fall between the surface of the body of water and the actual bottom of the vessel. However, once significant wave height has been exceeded, the ocean swells impact on the bottom of the hull producing violent movements.
Ground effect crafts have been used by European countries with some success. However, due to the large wing span of these crafts in addition to congested harbors and limited payload capacity in smaller versions of the crafts, ground effect crafts have not proven to be practical.
Catamarans are a very popular alternative for the ocean transportation industry. The success of catamarans or catamaran-type crafts vary greatly depending on the severity of the seas in which they operate. In a catamaran, twin hulls having narrow cross sections where wave contact is anticipated are designed so that the added hull buoyancy caused by waves will be minimized. The catamaran is attractive because of its simplistic design, high speed capability, fuel efficiency, and low cost of maintenance and operation. Unfortunately, the catamaran is generally unable to produce the same ride quality of some of the crafts described above. Furthermore, due to its resulting low displacement hull, cargo carrying capacity is restricted.
The swath vessel, a relative of the catamaran, has a small water-plane area twin hull or swath design with the twin hulls of the catamaran, torpedo shaped displacement chambers of a submarine, and the fins of a hydrofoil. This type of vessel has the ability to deliver a good quality ride while operating in choppy seas. Due to the significant reduction in pitching and rolling, sea sickness is virtually eliminated. As a light ship the swath vessel floats on its torpedo shaped hulls. The vessel""s torpedo hulls are partially or fully flooded with water, weighing the vessel down to its designed water line. The vessel is then supported by the remaining buoyancy in the torpedo hulls in addition to the added buoyancy of the catamaran hulls. Due to the long, narrow width of the catamaran hulls, the pounds per inch of immersion are low while the weight below the surface of the water is high and completely unbalanced. If the vessel displaces 1,000 pounds per inch of immersion, this unbalanced condition would permit the vessel to push through a one foot wave with 12,000 pounds of lift. This force is counter-balanced by the water ballast in the torpedo, resulting in slower vertical acceleration of the vessel and a good quality ride. Unfortunately, a good quality ride is provided at the expense of a good power to weight ratio. Although an uneconomical power to weight ratio is not a critical problem at low speeds, for high speed applications the power required to push the vessel and the accompanying weight of the water ballast becomes very costly with respect to fuel and machinery. Consequently, few swath-type high speed vessels are in current operation due to this problem.
U.S. Pat. No. 5,325,804 issuing to Schneider on Jul. 5, 1994 discloses a watercraft having twin submarine hulls supported by stanchions which extend between the cabin and the submarine hulls. The motor is supported by swing bars which raise and lower the engine.
U.S. Pat. No. 4,541,356 issuing to Jone on Sep. 17, 1985 discloses a multi-hull vessel having first and second tubes extending from a center keel, with outriggers extending on each side of the central hull.
U.S. Pat. No. 3,481,296 issuing to Stephens on Dec. 2, 1969, discloses a vessel having water ballast ducts in catamaran type pontoons. The flow of air and water is controlled by gates located at the bow and stem.
U.S. Pat. No. 1,444,150 issuing to Gadowski on Feb. 6, 1923 discloses a ship""s hull having a water passage on each side wall of the hull at a location beneath the waterline, to aid in stabilizing the vessel.
It is therefore an object of the invention to provide an improved vessel hull design incorporating a continuous flow ballast system design for countering dynamic wave forces.
It is also an object of the invention to provide an improved vessel hull design that enables a good quality ride on a body of water in both high and low speed applications in a cost-effective manner.
It is also an object of the invention to provide an improved vessel hull design that enables efficient and relatively low cost operation and maintenance of the vessel.
In the broader aspects of the invention, this sea friendly hull shape invention provides the benefit of water ballast without the penalty of carrying that ballast. There are open ballast passages which can be in the shape of pipes, or other similar shapes, through which water flows continuously when the vessel is in motion or at rest. The passages are connected to a main hull by thin wave piercing hull shapes. As a wave passes under the vessel, there is little area presented to increase the hull""s displacement and any hull movement up or down will be countered by the force of the water going through the ballast passages. In this manner there is a reaction similar to one offered by static ballast, but without the power demand needed to carry it.